Update HIP-Clang build instruction (#1764)

INSTALL.md

@@ -42,20 +42,43 @@ apt-get install hip-hcc
 
 * Install the [rocm](http://gpuopen.com/getting-started-with-boltzmann-components-platforms-installation/) packages.  ROCm will install some of the necessary components, including the kernel driver, HSA runtime, etc.
 
-* Build LLVM/clang/lld by using the following repository and branch and following the general LLVM/clang build procedure. It is recommended to use -DCMAKE_INSTALL_PREFIX=/opt/rocm/llvm with cmake so that LLVM/clang/lld are installed to the default path expected by hipcc.
+* Build HIP-Clang
+
+```
+git clone https://github.com/llvm/llvm-project.git
+cd llvm-project/llvm/tools
+ln -s clang ../../clang
+ln -s lld ../../lld
+cd ../..
+mkdir -p build && cd build
+cmake -DCMAKE_INSTALL_PREFIX=/opt/rocm/llvm -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=1 -DLLVM_TARGETS_TO_BUILD="AMDGPU;X86" ../llvm
+make -j
+sudo make install
+```
 
-   * LLVM: https://github.com/RadeonOpenCompute/llvm.git amd-common branch
-   * clang: https://github.com/RadeonOpenCompute/clang amd-common branch
-   * lld: https://github.com/RadeonOpenCompute/lld amd-common branch
-   
 * Build Rocm device library
 
-   * Checkout https://github.com/RadeonOpenCompute/ROCm-Device-Libs.git master branch and build it with clang built from the last step.
-   
+```
+export PATH=/opt/rocm/llvm/bin:$PATH
+git clone -b master https://github.com/RadeonOpenCompute/ROCm-Device-Libs.git
+cd ROCm-Device-Libs
+mkdir -p build && cd build
+CC=clang CXX=clang++ cmake -DLLVM_DIR=/opt/rocm/llvm -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_WERROR=1 -DLLVM_ENABLE_ASSERTIONS=1 ..
+make -j
+sudo make install
+```
+
 * Build HIP
 
-   * Checkout https://github.com/ROCm-Developer-Tools/HIP.git master branch and build it with HCC installed with ROCm packages. Please use -DHIP_COMPILER=clang with cmake to enable hip-clang.
-   
+```
+git clone -b master https://github.com/ROCm-Developer-Tools/HIP.git
+cd HIP
+mkdir -p build && cd build
+cmake -DCMAKE_INSTALL_PREFIX=/opt/rocm/hip -DHIP_COMPILER=clang -DCMAKE_BUILD_TYPE=Release ..
+make -j
+sudo make install
+```
+
 * Default paths and environment variables:
 
    * By default HIP looks for HSA in /opt/rocm/hsa (can be overridden by setting HSA_PATH environment variable)